PWA update available notification (#42)

src/ServiceWorker/events.json

@@ -0,0 +1,3 @@
+{
+  "SW_UPDATED": "swUpdated"
+}

src/ServiceWorker/sw.js

@@ -19,3 +19,24 @@ workbox.routing.registerRoute(
 	new RegExp('.*'),
     new workbox.strategies.StaleWhileRevalidate()
 );
+
+// This code listens for the user's confirmation to update the app.
+self.addEventListener('message', (e) => {
+	if (!e.data) {
+		return;
+	}
+
+	switch (e.data) {
+		case 'skipWaiting':
+			self.skipWaiting();
+			break;
+		default:
+			// NOOP
+			break;
+	}
+});
+
+workbox.core.clientsClaim();
+// The precaching code provided by Workbox.
+self.__precacheManifest = [].concat(self.__precacheManifest || []);
+workbox.precaching.precacheAndRoute(self.__precacheManifest, {});